A good memory is typically seen as a powerful advantage, an aid to intelligence and socializing. But when experience is traumatic, this asset may become a serious liability, according to new research on survivors of the Rwandan genocide.

Researchers at the University of Basel in Switzerland studied a gene for a protein called PKCA, which is known to be involved in the encoding of emotional memories. In healthy Swiss adults, a variant called rs4790904 was found to be associated with visual memory.

There are three versions of rs4790904: AA, AG and GG. In one experiment including over 700 healthy adults from Switzerland, people with the AA variant had better recall of happy or otherwise emotionally positive and neutral images. A brain imaging experiment including nearly 400 Swiss adults also linked the AA version with improved memory for pictures with either a positive or negative emotional tone.

Researchers then studied the same gene in 347 adult Rwandan refugees who were living at the Nakivale refugee camp in Uganda. All of them had been exposed to the trauma of the 1994 Rwandan genocide, which had forced them to flee their homes. Around 800,000 people were slaughtered in 100 days during the genocide, when Hutu militias and gangs attacked the minority Tutsi population and those sympathetic to them.

Thirty-nine percent of the refugees had current symptoms of post-traumatic stress disorder (PTSD), an anxiety disorder marked by a sense of repeatedly re-experiencing the emotional and physical sensations linked to the trauma, often triggered by sensory reminders of the event, like sudden loud noises. People with PTSD typically try to avoid these cues, which can result in isolation and increased distress.

Rwandan refugees with the AA variant were more likely to have PTSD than those with the other versions of the gene — particularly symptoms of re-experiencing the traumatic event, like flashbacks. Avoidance of trauma reminders was also more common in those with the AA version.

According to the study, which was published in the Proceedings of the National Academy of Sciences, the findings point to a “genetic link between the predisposition to build strong memory and the risk for PTSD.”

The research also adds to increasing evidence that many “positive” genes also have a downside — and similarly, many “negative” ones have an upside. For example, one gene linked with a tendency for children to share treats with others is also linked to ADHD and later in life, promiscuity and addiction.

The genetics of autism similarly seem to show a mix of increased vulnerabilities and strengths. In fact, the “intenseworld” theory of autism suggests that the condition may result from having a brain that takes in too much, resulting in difficulty accommodating the overload of sensations, associations and memories. This could result in a sensitive type of higher intelligence, which can simultaneously lead to withdrawal and repetitive behaviors in an attempt to impose order on the overwhelming input.

When we contemplate enhancing memory, it’s important to consider that this will strengthen our recall of disaster and pain, not just success and pleasure. There’s no free lunch, it seems.